U.S. Pat. No. 9,359,981 discloses an outboard motor including a system for enhancement of a first subset of sounds having a desired frequency, and a method for modifying sounds produced by an air intake system for an internal combustion engine powering the outboard motor. The method includes collecting sounds emitted in an area proximate a throttle body of the engine. A first subset of the collected sounds, which have frequencies within desired frequency range, is then amplified. The amplified first subset of sounds is then transmitted to an area outside a cowl covering the engine.
U.S. Pat. No. 9,376,195 discloses an outboard motor comprising an engine having an exhaust gas discharge opening, a midsection housing coupled below and supporting the engine, and an exhaust pipe having an exhaust inlet in fluid communication with the exhaust gas discharge opening. The exhaust pipe extends downwardly to a primary exhaust outlet. An idle relief port in the exhaust pipe is located in a fluid path between the exhaust inlet and the primary exhaust outlet. A sound-attenuating plenum chamber has an interior that is in fluid communication with an interior of the exhaust pipe by way of the idle relief port. The plenum chamber is a separate component that is exterior to the midsection housing, and exhaust gas flows from the interior of the exhaust pipe to the interior of the plenum chamber without first flowing through the midsection housing.
U.S. Pat. No. 9,944,376 discloses exhaust systems for outboard marine engines that are configured to propel a marine vessel in a body of water. An intermediate exhaust conduit is configured to receive the exhaust gas from the primary exhaust conduit. A primary muffler receives the exhaust gas from a intermediate exhaust conduit. A secondary muffler receives the exhaust gas from the primary muffler. An idle relief outlet discharges the exhaust gas from the secondary muffler to atmosphere. A bypass valve is positionable into an open position wherein the exhaust gas is permitted to bypass the secondary muffler and flow from the primary muffler to the idle relief outlet and into a closed position wherein the exhaust gas is not permitted to bypass the secondary muffler and instead flows from the primary muffler to the idle relief outlet via the secondary muffler.
U.S. Pat. No. 10,180,121 discloses an outboard motor including an internal combustion engine and a cowl covering the engine. An air vent allows intake air into the cowl, an air intake duct routes the intake air from the air vent to the engine, and a throttle body meters flow of the intake air from the air intake duct into the engine. A sound enhancement device is located proximate the throttle body. A sound duct is provided, and has an inlet end located proximate the sound enhancement device and an outlet end located proximate an outer surface of the cowl. The sound enhancement device is tuned to amplify a first subset of sounds having a desired frequency that are emitted from the throttle body, and the sound duct transmits the amplified sounds to an area outside the cowl. A method for modifying sounds produced by an air intake system of an outboard motor is also provided.
U.S. Pat. No. 9,909,545 discloses an outboard motor including an internal combustion engine powering the outboard motor and a cowl covering the engine and having a vent allowing air under the cowl. A throttle body meters flow of the air into the engine and an intake structure downstream of the throttle body delivers the metered airflow to one or more combustion chambers in a cylinder block of the engine. A sound enhancement assembly in acoustic communication with the intake structure collects sounds emitted by the engine. The sound enhancement assembly is configured to amplify a subset of the collected sounds that have frequencies within a desired frequency range. A method for modifying sounds produced by an air intake system of an internal combustion engine powering an outboard motor is also disclosed. The method includes positioning a sound enhancement assembly in acoustic communication with an air intake passageway located downstream of the engine's throttle body.
The above patents and patent applications are hereby incorporated by reference herein in their entireties.